Typically, a reference value of an amount of a fuel fed to an engine is predetermined according to an engine speed, a throttle valve opening degree, etc. A controller for controlling the operation of the engine is configured to determine the fuel feed amount determined as the reference value based on the engine speed, the throttle valve opening degree, etc. obtained from sensors, and to cause a fuel injector to feed the determined amount of fuel to the intake-air.
In recent years, the engine uses fuel feed stop control for stopping fuel feeding to the engine when the engine is in a predetermined deceleration state, to improve fuel consumption efficiency and reduce an exhaust gas (see, e.g., Japanese Laid-Open Patent Application Publication No. 2005-76600.) When a clutch is disengaged during the fuel feed stop control, an inertia force of a drive wheel is not transmitted to the engine and an engine stall tends to occur. Therefore, in a state where the clutch is disengaged, the fuel feeding to the engine is resumed.
At a time point when a clutch switch for detecting a clutch state is in a state near a boundary between an ON-state and an OFF-state, an ON-signal and an OFF-signal are output alternately in a very short time period. In this case, stopping of the fuel feeding and starting of the fuel feeding may be undesirably repeated in a very short time period. This phenomenon is called “chattering.” To avoid this, the fuel feed stop control is not initiated promptly, even if the fuel feed stop condition is satisfied immediately after the fuel feeding to the engine is resumed, but is initiated after a lapse of a predetermined time. Thus, responsiveness to the initiation of the fuel feed stop control is set low.
When a driver disengages the clutch to downshift a transmission gear position in a decelerated state, an engine stall will not occur if the fuel feed stop control is continued because a time period when the driver operates the clutch to disengage it is very short. However, the fuel feeding to the engine is resumed although the time period when the clutch is disengaged by the driver is very short. Once the fuel feeding to the engine is resumed, the fuel feeding continues for some time to inhibit “chattering,” even if the fuel feed stop condition is satisfied again. This results in wasteful fuel feeding. As a result, fuel consumption efficiency and exhaust gas capability are reduced.